Semiconductor devices are found in many products in the fields of entertainment, communications, networks, computers, and household markets. Semiconductor devices are also found in military, aviation, automotive, industrial controllers, and office equipment. The semiconductor devices perform a variety of electrical functions necessary for each of these applications.
The manufacture of semiconductor devices involves formation of a wafer having a plurality of die. Each semiconductor die contains hundreds or thousands of transistors and other active and passive devices performing a variety of electrical functions. For a given wafer, each die from the wafer typically performs the same electrical function. Front-end manufacturing generally refers to formation of the semiconductor devices on the wafer. The finished wafer has an active side containing the transistors and other active and passive components. Back-end manufacturing refers to cutting or singulating the finished wafer into the individual die and then packaging the die for structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce a package suitable for faster, reliable, smaller, and higher-density integrated circuits (IC) at lower cost. Flip chip packages or wafer level chip scale packages (WLCSP) are ideally suited for ICs demanding high speed, high density, and greater pin count. Flip chip style packaging involves mounting the active side of the die facedown toward a chip carrier substrate or printed circuit board (PCB). The electrical and mechanical interconnect between the active devices on the die and conduction tracks on the carrier substrate is achieved through a solder bump structure comprising a large number of conductive solder bumps or balls. The solder bumps are formed by a reflow process applied to solder material deposited on contact pads which are disposed on the semiconductor substrate. The solder bumps are then soldered to the carrier substrate. The flip chip semiconductor package provides a short electrical conduction path from the active devices on the die to the carrier substrate in order to reduce signal propagation, lower capacitance, and achieve overall better circuit performance.
Some semiconductor devices have optically active regions. The optical devices react to light and generate electrical signals in response thereto. The electrical signals are processed by other active and passive circuits within the semiconductor device. The light must pass through the semiconductor package to reach the optical devices. In some devices, the light passes through an opening in the substrate, such as described in U.S. Pat. No. 6,765,236. The process of forming the opening in the substrate and confirming alignment for the passage of light to the optical devices adds manufacturing steps and complexity. In addition, the semiconductor package typically has underfill material and molding compound for structural integrity and environmental protection. Care must be taken when applying the underfill material and molding compound to avoid blocking the passage of light to the optical devices.
A need exists for a simple process to make optical semiconductor packages without interfering with the passage of light to the optical devices.